This invention relates to an in-line electron gun structure for color cathode ray tubes (CCRT), and more particularly relates to an improved lensing arrangement whereby the effective apertures of the final and focusing accelerating electrode lenses are increased.
Reducing the diameter of the necks of CCRTs can lead to cost savings for the television set maker and user in enabling smaller beam deflection yokes and consequent smaller power requirements. However, reducing neck diameter while maintaining or even increasing beam deflection angle and display screen area severely taxes the performance limits of the electron gun.
In the conventional, in-line electron gun design, an electron optical system is formed by applying critically determined voltages to each of a series of spatially positioned apertured electrodes. Each electrode has at least one planar apertured surface oriented normal to the tube's long or Z axis, and containing three side-by-side or "in-line" circular straight-through apertures. The apertures of adjacent electrodes are aligned to allow passage of the three(red, blue and green) electron beams through the gun.
As the gun is made smaller to accommodate the so-called "mini-neck" tube, the apertures are also made smaller and the focusing or lensing aberrations of the apertures are increased, thus degrading the quality of the resultant picture on the display screen.
Various design approaches have been taken to attempt to increase the effective apertures of the gun electrodes. For example, U.S. Pat. No. 4,275,332, and U.S. patent application Ser. No. 303,751, filed Sept. 21, 1981 and assigned to the present assignee, describe overlapping lens structures. U.S. Ser. No. 463,791, filed Feb. 4, 1983 and assigned to the present assignee, describes a "conical field focus" lens arrangement. Each of these designs is intended to increase effective apertures in the main lensing electrodes and thus to maintain or even improve gun performance in the new "mini-neck" tubes.
It is an object of the present invention to provide an alternate electron gun structure which has increased effective apertures in the main lensing electrodes, but which does not rely on overlapping lenses or a "conical field focus" arrangement.